1. Field of the Invention
The present invention relates to a liquid discharging head, which discharges the liquid by acting a thermal energy on the liquid to generate bubbles, a method of producing the same, and liquid discharging apparatus which uses the same head.
The present invention is applicable to devices, e.g., a printer and copier recording images on a printing medium (e.g., paper, yarn, fiber, cloth, leather, metal, plastic, glass, lumber and ceramic), a facsimile having a communication system, a word processor having a printer, and an assembly in which an industrial recording device is combined with a varying processing device.
The term xe2x80x9crecordingxe2x80x9d used herein not only refers to forming a meaning image (e.g., letter, pattern or the like) on a recording medium but also a meaningless image (e.g., pattern).
2. Related Background Art
The ink jet recording method is known for recording devices, e.g., printer. This method, also known as bubble jet recording method, gives energy (e.g., heat) to a liquid ink flowing in a flow passage to generate bubbles, rapid volumetric change as a result of which is used to discharge the ink from the discharge port onto a recording medium to form an image thereon. The recording device which is based on the bubble jet recording method generally has an ink discharge port from which the ink is discharged, an ink passage leading to the discharge port, and an electrothermal converter as the energy-generating means needed for discharging the ink in the passage, as disclosed by, e.g., U.S. Pat. No. 4,723,129.
This type of recording method has various advantages, e.g., giving a high-quality image quickly at low noise, and also easily giving a high-resolution recording image and color image by a compact device, because of its head being provided with ink discharge ports at a high density. Therefore, the bubble jet recording method recently has been massively going into various office devices, e.g., printers, copiers and facsimiles, and even into industrial systems, e.g., textile printers.
As the bubble jet techniques are finding wider use in various areas, they are increasingly required to have higher functions, for which various proposals have been made, e.g., driving conditions for improved liquid discharging methods which allow higher ink discharging speed and better ink discharging based on stable bubble generation for higher-quality images, and improved ink flow passage shapes for a liquid discharging head which secures faster refill of the discharged liquid into the passage.
For the head in which the bubbles are generated and grown in the nozzle to discharge the liquid, it is known that growth of the bubbles away from the discharge port and the resultant liquid flow deteriorate discharging energy efficiency and refill characteristics. The structures to improve discharging energy efficiency and refill characteristics are disclosed by European Patent Application Laid-Open Specification EP0436047A1.
The above invention has the first valve between the vicinity of the discharge port and a bubble generating section to completely cut off them from each other, and second valve between the bubble generating section and ink supply section also to completely cut off them from each other, wherein these valves open or close alternately (FIG. 4 to FIG. 9 in EP436047A1 specification). For example, referring to FIG. 14 in this specification, which is FIG. 7 in the EP436047A1 specification, the heat generating member 110 is provided almost at the center of the ink passage 112 running between the ink tank 116 and nozzle 115, the ink tank 116 being on the base plate 125 which forms the inner wall for the ink passage 112. The heat generating member 110 is encased in the totally closed compartment 120 in the ink passage 112. The ink passage 112 is composed of the base plate 125 directly coated with the thin films 123 and 126 placed one on another, and tongue-like pieces 113 and 130 as the closing bodies. The tongue-like piece in the open condition is shown in FIG. 31 by the dotted lines. The thin film 123, running in the plane in parallel to the base plate 125 and terminating at the stopper 124, covers the ink passage 112. As the bubbles are generated in the ink, the free end of the tongue-like piece 130 in the nozzle area, in closely contact with the stopper 126 while it is stationary, moves upward, and the ink liquid in the compartment 120 is ejected from the nozzle 115 via the ink passage 112. In this case, the ink liquid in the compartment 120 is prevented from moving towards the ink layer 116, because the tongue-like piece 113 in the ink layer 116 area comes into close contact with the stopper 124 while it is stationary. The tongue-like piece 130 moves downward, as the bubbles in the ink disappear, and comes into close contact with the stopper 126 again. Then, the tongue-like piece 113 falls in the ink compartment 120, allowing the ink liquid to flow into the compartment 120.
The invention disclosed in EP0436047A1 has several disadvantages. For example, the ink following the bubbles significantly trails while it is discharged, because two out of the three compartments of near the discharge port, bubble generating section and ink supply section are separated from each other, producing a fairly larger quantity of the satellite dots than the conventional discharging method involving growth, shrinkage and disappear of the bubbles. This trouble conceivably results from loss of the effect of meniscus retreat accompanying disappear of the bubbles. Another disadvantage is dissipation of large quantity of energy for discharging the ink, when the valve on the bubble discharge side is closed. Still other disadvantages are large fluctuation of size of the discharged liquid droplets and extremely low discharge response frequency, which make the invention impractical. These problems come from its structure: the compartment is refilled to make up the ink to be supplied to the nozzle as the bubbles in the liquid disappear in the bubble generating section, and the vicinity of the discharge port cannot be supplied with the liquid until the new bubbles are generated.
The present invention provides an innovative method and head structures which simultaneously satisfy the characteristics running counter to each other; improved efficiency of controlling growth of the bubble component away from the discharge port, and improved refill efficiency and characteristics, based on the new concept. They also satisfy requirements for improved discharging efficiency.
The inventors of the present invention have found, after having extensively studied to satisfy the above requirements, that growth of the bubbles away from the discharge port (i.e., towards the rear side) is controlled by the special check valve function in the straight nozzle structure in the liquid-discharging head, where the liquid is discharged as the bubbles grow, and that the discharging energy towards the rear side can be effectively utilized for the discharge port side. They also have found that controlling growth of the bubble component towards the rear side by the special check valve function can increase discharge response frequency to an extremely high level.
It is an object of the present invention to simultaneously improve discharge power and discharge frequency by the nozzle structure and discharging method incorporating a novel valve function, and thereby to establish the novel discharging formula (structure) for a head which can produce higher-quality images at a higher speed than the conventional one can achieve.
In order to achieve the above objects, the liquid discharging head of the present invention is provided with a discharge port for discharging the liquid, liquid passage provided with bubble-generating means for generating the bubbles in the liquid supplied via a liquid supply port, and in communication with the discharge port at its one end, and movable member arranged apart from the discharge port by a gap in the liquid passage for the bubble-generating means, wherein the projected area of the movable member on the liquid supply port is larger than the opening area of the liquid supply port; the bubble-generating means is arranged on the wall, via the movable member, facing the wall to which the liquid supply port in the liquid passage is open; the movable member is on the one end of the liquid passage as the fulcrum and its free end is arranged on the closed side of the liquid passage; the bubble-generating means is arranged to face the free end of the movable member in the same direction; the liquid supply port is open to the liquid passage on the side of the fulcrum for the movable member; and the discharge port is positioned on the side of the fulcrum for the movable member.
In the above liquid discharging head, the bubbles when generated by the bubble-generating means in the liquid passage produces pressure waves, which displace the free end of the movable member, to substantially close the liquid supply port by the movable member, where the movable member is supported by one end of the liquid passage as the fulcrum, and the discharge port is in communication with the liquid passage in the area of the fulcrum for the movable member. Therefore, volume of the liquid passage little increases even when the movable member is displaced, with the result that most of the pressure waves produced by the bubbles propagate towards the discharge port, to greatly increase discharge power. As a result, good discharge can be secured, even when a viscous liquid is used or the liquid increases in viscosity under the changed environments. The liquid little moves towards the liquid supply port, because of the liquid supply port being substantially closed, thereby controlling retreat of the meniscus at the discharge port which has discharged the liquid. As a result, the meniscus recovers quickly after the liquid is discharged, and discharging (driving) frequency can be drastically increased when the liquid is to be discharged accurately (at a constant rate).
The liquid discharging head of the present invention is provided with a discharge port for discharging the liquid, liquid passage provided with bubble-generating means for generating the bubbles in the liquid supplied via a liquid supply port, and in communication with the discharge port at its one end, and movable member arranged apart from the discharge port in the liquid passage for the bubble-generating means, wherein the projected area of the movable member on the liquid supply port is larger than the opening area of the liquid supply port; the liquid passage is in communication with the discharge port at one end; the movable member is supported by the fulcrum on the side where the bubbles generated by the bubble-generating means greatly grow, and has the free end on the side where growth of the bubbles is controlled; the liquid supply port is open to the liquid passage on the side of the fulcrum for the movable member; and the movable member substantially closes the liquid supply port as the bubbles are generated by the bubble-generating means. The liquid discharging head of this design propagates the pressure waves produced by the bubbles in a concentrated manner towards the discharge port positioned on the side of the fulcrum for the movable member, to discharge the liquid through the discharge port, and displaces the free end of the movable member towards the bubble-generating means side as the bubbles disappear and allows the liquid supply port positioned on the side of the fulcrum for the movable member to come in communication with the liquid passage, to supply the liquid to the liquid passage via the liquid supply port.
In the above liquid discharging head, the bubbles generated by the bubble-generating means produce the pressure waves, which displace the free end of the movable member to substantially close the liquid supply port by the movable member. The bubbles largely grow towards the discharge port side but their growth in the opposite direction is controlled in the liquid passage, with one end in communication with the discharge port and the other end being closed. Since the movable member has the fulcrum on the side where the bubbles largely grow and the free end on the side where growth of the bubbles is controlled as in the case of the liquid discharging head, most of the pressure waves produced by the bubbles is directed towards the discharge port side to drastically increase discharging power. The liquid supply port is substantially closed, and the bubbles on the closed side in the liquid passage, as the bubble-generating area where the bubbles are generated by the bubble-generating means, start to disappear faster than those in the bubble-generating area on the discharge port side, causing the liquid flow from the liquid supply port into the liquid passage, and, at the same time, displacing the movable member towards the bubble-generating area, with the result that the meniscus recovers quickly after the liquid is discharged and, hence, discharging frequency drastically increases.
It is preferable for the liquid discharging head of the present invention to have the discharge port positioned on the side of the fulcrum for the movable member, and the liquid supply port open to the liquid passage also on the side of the fulcrum for the movable member. The movable member substantially closes the liquid supply port side in the liquid passage during the initial stage of bubbling in the bubble-generating area. It is difficult for, e.g., the action of recovering by keeping the discharge port side at a vacuum to easily remove the residual bubbles, when these bubbles produced during the bubbling process remain in the closed space in the liquid passage. On the other hand, the present invention can remove the residual bubbles, because the movable member has the free end at the position where the liquid passage is closed, and the liquid passage is refilled with the liquid from the closed bubble-generating area in the liquid passage via the liquid supply port, as the free end of the movable member is displaced, improving the discharge characteristics of the liquid discharging head and its reliability.
The liquid discharging apparatus of the present invention is provided with the above-described liquid discharging head of the present invention and a carrying means for carrying the recording medium which receives the liquid discharged from the liquid discharging head, to record images on the recording medium with the ink discharged from the liquid discharging head.
The method for discharging liquid of the present invention is a liquid discharging method for the liquid discharging head provided with a discharge port for discharging the liquid, bubble-generating means for generating the bubbles to discharge the liquid from the discharge port, liquid passage whose one end is in communication with the discharge port and the other end is closed, liquid supply port in the liquid passage to supply the liquid to the passage, and movable member arranged apart from the discharge port in the liquid passage side for the bubble-generating means, wherein the projected area of the movable member on the liquid supply port is larger than the opening area of the liquid supply port; the movable member substantially closes the liquid supply port as the bubbles are generated by the bubble-generating means; the bubbles largely grow towards the discharge port side while being controlled to grow towards the closed side of the liquid passage, to discharge the liquid from the discharge port; and the free end of the movable member is displaced towards the bubble-generating means side as the bubbles disappear, and the liquid supply port positioned on the side of the fulcrum for the movable member comes in communication with the liquid passage, to cause flow of the liquid via the liquid supply port from the fulcrum side to the free end side of the movable member on the liquid supply port side of the movable member, and also from the free end side to the fulcrum side of the movable member on the bubble-generating means side of the movable member, to supply the liquid to the liquid passage.
The present invention also provides a method of producing the liquid discharging head, which is provided with a discharge port for discharging the liquid, bubble-generating means for generating the bubbles in the liquid supplied via the liquid supply port, liquid passage in communication with the discharge port, and movable member arranged apart from the supply port in the liquid passage for the bubble-generating area, wherein the projected area of the movable member on the liquid supply port is larger than the opening area of the liquid supply port. This method comprises several steps of forming the first gap-forming member for forming a gap on the first base plate between the liquid supply port and movable member; forming a film of a material which serves as the material for the movable member, which covers the first base plate and first gap-forming member; patterning the above film into a cantilever shape with one end as the fulcrum on the liquid passage side and the other end as the free end; forming the second gap-forming member in the liquid passage on the above film; forming the wall member as the side wall of the liquid passage on the above film and second gap-forming member; flattening the second gap-forming member and side wall in such a way that they form one plane; forming the second base plate containing the bubble-generating means on the flattened second gap-forming member and side wall; forming the discharge port in the section of the second base plate corresponding to one end of the liquid passage; opening the first base plate to form the liquid supply port having a smaller opening area than the projected movable member; and removing the first gap-forming member, and second gap-forming member via the liquid supply and discharge ports.
The above method can produce the liquid discharging head of greatly improved discharging power and frequency, as discussed above.
The other effects of the present invention can be understood, as they are described in the preferred embodiments, described later.
The terms xe2x80x9cupstreamxe2x80x9d and xe2x80x9cdownstreamxe2x80x9d described herein are related to a direction of flow of the liquid from the liquid supply source to the discharge port via the bubble-generating area (or movable member), or to such a direction in terms of configuration.
The xe2x80x9cdownstream sidexe2x80x9d of the bubbles themselves means those generated downstream of the above flow or configuration direction with respect to the bubble center or area center of the heat generating member.